JWST/MIRI Imaging Search for Kinematically Detected Protoplanetary Candidates

Abstract

Kinematic perturbations observed with the Atacama Large Millimeter/submillimeter Array in CO line emission provide evidence for a population of embedded giant protoplanets shaping the structure of protoplanetary disks. We present JWST/MIRI F1140C (λ = 11.3 μm) coronagraphic observations of five protoplanetary disks—HD 163296, RXJ 1615.3–3255, RXJ 1842.9–3532, SY Cha, and LkCa 15—with the goal of directly detecting candidate protoplanets orbiting at ≳70 au that were previously inferred from gas kinematics. The data were analyzed using a bespoke methodology that combines subtraction of a reference point-spread function with forward modeling of partially resolved inner disk emission, which otherwise dominates the diffraction pattern in the images. This approach improves the sensitivity to young companions at small separations. No point source consistent with an embedded protoplanet is detected in any of the systems. Instead, in three systems we detect extended emission at 11.3 μm tracing the outer disk out to radii comparable to those probed by CO. Injection tests indicate upper mass limits of roughly 3–20 MJ at separations of a few hundred astronomical units, assuming no additional thermal contribution from the circumplanetary environment. Even with space-based observations, these limits remain mostly above the ∼1–5 MJ masses inferred from disk kinematics, largely due to the limitations imposed by emission (and/or scattered light) contributions from both the inner disk and outer disk. These observations highlight the challenges of observing protoplanets embedded in their forming environment at large separation with JWST/MIRI. Lessons learned can inform future studies with the Extremely Large Telescope, which will probe separations where the occurrence rate of gas giants is expected to be higher.